1. Field of the Invention
The present invention is related to data communications. In particular, the present invention is related to providing router redundancy in a statically configured routing environment for multiple protocols using the virtual router redundancy protocol (VRRP).
2. Description of the Related Art
The Transport Control Protocol/Internet Protocol (TCP/IP) suite of data communication protocols is used in many of today""s internetnetworks (internets). A TCP/IP-based internet provides a data packet switching system for communication between nodes (e.g., end-user workstations, servers, network devices, etc.) connected to the internet. With reference to FIG. 1, International Standards Organization (ISO) Open Systems Interconnection (OSI) Network-layer devices 105, 110, and 140, known as routers or switches, select a path and forward, i.e., route, IP datagrams between nodes connected to the internet 100. For example, internet 100 includes local area networks (LANs) 101 and 151, and wide area network (WAN) 102 interconnected by routers 105, 110 and 140. The routers route IP datagrams, for example, between nodes 115, 120, 125 and 130 attached to LAN 101 and nodes 145 and 150 attached to LAN 151.
As can be seen from FIG. 1, routers 105 and 110 provide multiple paths for transmitting IP datagrams from nodes on LAN 101 to nodes on other IP networks in the internet. To prevent generating and forwarding duplicate IP datagrams over the internet, each of the nodes on LAN 101 transmits a unicast IP datagram to only one of routers 105 and 110 as a next hop, or first hop, router. The next hop router forwards the datagram to a node on another IP network in the internet that is reachable via the router. As is well known in the art, a next hop router can be statically configured at each node as the default router (also referred to as the default gateway) towards another IP network. However, a static default router configuration provides a single point of failure in the event the default router becomes unavailable. To overcome this problem, next hop routers can be dynamically configured at each node, using a dynamic routing protocol such as the well known Routing Information Protocol (RIP) or Open Shortest Path First (OSPF) dynamic routing protocols. However, the reliability provided by a dynamic routing protocol is at the expense of node and router processing overhead, network overhead, interoperability problems, etc.
The single point of failure inherent in a static next hop router configuration can be overcome through the use of the Virtual Router Redundancy Protocol (VRRP). VRRP, as set forth in the Internet Society""s Request For Comments 2338, April, 1998, is an election protocol that assigns responsibility to a master virtual router, wherein the master virtual router is one of two or more VRRP based routers attached to a LAN. VRRP provides dynamic fail-over in forwarding responsibility if the master virtual router, selected as one of the two or more VRRP routers on the LAN, becomes unavailable. In essence, and as explained in detail in RFC 2338, VRRP provides a redundant, relatively more reliable default path for transmission of IP datagrams destined to nodes on other EP networks.
For a better appreciation and understanding of the present invention, a brief review of the VRRP protocol follows. In the network illustrated in FIG. 2, routers 105 and 110 operate according to the VRRP. VRRP is based on the concept of a virtual router, which is an abstract object that operates as a default router for nodes attached to the LAN, and for which a single well known IEEE 802.3 MAC (Media Access Control) address is assigned. In network 100, two virtual routers are configured: virtual router 1, and virtual router 2. In general, the scope of a virtual router is restricted to a single LAN, and each virtual router comprises a master and one or more backup routers. For example, router 105 is the master virtual router and router 110 is the backup virtual router for virtual router 1. The master and backup virtual routers share the same virtual router identifier (VRID=1), same IP address (IP=A), and the same VRRP-based MAC address (00-00-5E-00-01-{VRID}(h), e.g., 00-00-5E-00-01-01(h)). Conversely, router 110 is the master virtual router and router 105 is the backup virtual router for virtual router 2, which has a VRID=2, IP address=B, and VRRP-based MAC address of 00-00-5E-00-01-02(h). In this example, nodes 115 and 120 are statically configured with a default next hop router IP address of xe2x80x9cAxe2x80x9d, while nodes 125 and 130 are statically configured with a default next hop router IP address of xe2x80x9cBxe2x80x9d. (Splitting the nodes between redundant routers in this manner provides load balancing and other advantages well known in the art).
In accordance with VRRP, the master virtual router functions as the forwarding router for the IP address associated with the virtual router. For example, router 105 is the master virtual router for virtual router 1, and forwards IP datagrams for the nodes having the IP address of virtual router 1 (IP address xe2x80x9cAxe2x80x9d) statically configured as the default next hop router. The master virtual router periodically transmits advertisements, formatted as IP multicasts, to the backup virtual router(s) on the local network to indicate to the backup(s) that it is still functioning as the master virtual router. (Use of IP multicast allows VRRP to be implemented in multiaccess LANs such as Ethernet, Fast Ethernet, Gigabit Ethernet, FDDI, Token Ring, ATM LAN emulation (ATM LANE), etc.) If master virtual router 1 fails, e.g., advertisements cease, the master-down_timer expires or a shutdown event is received at the backup virtual router 1, backup virtual router 1 takes over as the new master virtual router 1, providing routing capability for nodes 115 and 120. Since both routers maintain the same IP address (xe2x80x9cIP Axe2x80x9d), and share the same VRRP based media access control (MAC) address, no reconfiguration of the static default next hop router IP address is required at each of the nodes that transmit IP datagrams to virtual router 1, destined for nodes on other IP networks. Likewise, if master virtual router 2 fails, backup virtual router 2 provides routing for nodes 125 and 130.
While the VRRP based network of FIG. 2 provides router redundancy and fail-over protection for nodes having statically configured default next hop router IP addresses, no such mechanism presently exists for protocol stacks other than TCP/IP. However, many of today""s internets are a connected amalgamation of heterogeneous, originally isolated, data communication networks, wherein the routers often times are required to support multiprotocol routing capabilities, including data communication protocols for which a default router election protocol such as VRRP is not available. For example, in the internet depicted in FIG. 2, nodes 115 and 125 communicate with each other as well as nodes reachable via router 105 using both IP and the well known Network layer protocol Internet Protocol eXchange (IPX), yet VRRP does not provide routing redundancy support for IPX. What is needed is a system in which nodes utilizing data communication protocols in addition to the Internet Protocol (IP) can obtain the benefits of VRRP without implementing a separate default router election protocol.
According to the present invention, nodes configured with data communication protocol suites other than TCP/IP, for which a default router election protocol such as VRRP is not available, nevertheless forward traffic destined to nodes on other network to the VRRP master virtual router. A non TCP/IP based node, given a statically configured Network layer address for a next hop router, resolves the Network layer address to a VRRP based MAC layer address for the next hop router, if the next hop router has VRRP enabled and is the master virtual router. The non TCP/IP node caches the VRRP based MAC address for use in forwarding non TCP/IP traffic to the appropriate next hop router. Thereafter, the non TCP/IP node forwards traffic destined to nodes on other networks to the VRRP master virtual router. If the master virtual router becomes unavailable to forward TCP/IP based traffic, it transitions to become the new backup virtual router, while the backup virtual router transitions to become the new master virtual router responsible for forwarding TCP/IP based traffic. The non TCP/IP based node, having cached the VRRP based MAC address of the next hop router, forwards traffic destined to nodes on other networks to the new master virtual router, which shares the same VRRP based MAC address as the former master virtual router.